Evidence for the involvement of several intracellular domains in the coupling of oxytocin receptor to G alpha(q/11).
In order to probe the nature of oxytocin receptor (OTR)/G alpha(q/11) protein coupling, we examined the effect of co-expression of OTR intracellular domains on oxytocin-stimulated phosphoinositide turnover in COSM6 cells overexpressing OTR and G alpha(q). Co-expression of G alpha(q) enhanced the oxytocin response maximally at a pOTR/pG alpha(q) plasmid transfection ratio of 1:0.16. In cells co-expressing OTR and G alpha(q/11), oxytocin stimulated phosphoinositide turnover with an EC50 of 48 nM. Co-transfection with plasmids expressing OTR intracellular domains inhibited oxytocin-stimulated phosphoinositide turnover by 23 +/- 6% (1i), 37 +/- 4% (2i), 55 +/- 6% (3i), and 40 +/- 6% (4i), respectively (P < 0.01). Expression of the 3i loop of the alpha(1B)-adrenergic receptor, which also couples to G alpha(q/11), inhibited phosphoinositide turnover by 35 +/- 2% (P < 0.01), while expression of the 3i loop of the dopamine 1A receptor, which couples to G alpha(s), had no effect. While these data indicate a functional role for the OTR 3i loop, they also suggest that interactions with more than one intracellular domain probably mediate the coupling of OTR to the G alpha(q/11) class of GTP-binding proteins.
Qian
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A
Department of Biochemistry and Molecular Biology, University of Texas Houston Medical School 77030, USA.
Wang
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W
Sanborn
B M
BM
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D010716:Phosphatidylinositols / Q000378:metabolism; D018045:Receptors, Oxytocin / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection
D010716:Phosphatidylinositols; D018045:Receptors, Oxytocin; D011994:Recombinant Proteins; D019204:GTP-Binding Proteins